Ultrasonic image recording system

ABSTRACT

An ultrasonic image recording system comprising a thin layer piezoelectric material for exposure to a field of ultrasonic radiation to be imaged and defining an image recording surface. A plurality of thin film field-effect transistors are distributed in an array on the piezoelectric material and are electrically connected in a crossbar arrangement to derive signals in succession from image points of the image recording surface.

United States Patent [1 1 Bonnet et a1.

ULTRASONIC IMAGE RECORDING SYSTEM Inventors: Dieter Bonnet, Eschborn; Helmut Rabenhorst, Frankfurt-Niederrad, both of Germany Assignee: Hoffmann-LaRoche Inc., Nutley,

Filed: Feb. 1, 1972 Appl. No.: 222,578

Foreign Application Priority Data Feb. 17, 1971 Germany 2107555 US. Cl. 340/5 MP, 310/8.l, 317/235 M Int. Cl. H04b 11/00 Field of Search 340/5 MP, 5 H, 10;

References Cited UNITED STATES PATENTS 6/1967 Fyler 340/5 MP June 18, 1974 3,460,005 8/1969 Kanda et al. 317/235 M 3,475,551 10/1969 Green et a1. 340/5 MP 3,675,472 7/1972 Kay et al 340/5 MP FOREIGN PATENTS OR APPLICATIONS 1,244,551 9/1971 Great Britain 340/5 H Primary Examiner-Richard A. Farley Attorney, Agent, or FirmSamuel L. Welt; Bernard S. Leon [5 7] ABSTRACT 5 Claims, 2 Drawing Figures PAIENIED JUN] 81974 FIG. 1

I FROM ALL DRA NS MF II, IIJTII +4- m m 1 L FIG. 2

POTENTIAL SOURCE TIMER BACKGROUND OF THE INVENTION This invention relates to an ultrasonic image recording system.

X-rays are still used practically exclusively at the present time to detect internal structures in human and animal tissue. Apart from the fact that the tissue is exposed to health risks due to high-energy radiation, the contrast of the optical images produced could be greatly improved upon.

An alternative to the use of X-rays is irradiation with ultrasonics, to which the different types of tissue are permeable to very different degrees and thus offer good contrast. This irradiation is also completely harmless provided the total radiation power is below the cavitation limit. Since the sound radiated by conventional ultrasonic sources is coherent, holographic recordings are possible, which enable the irradiated tissue to be viewed stereoscopically, and this is very important, for example, for detection of the position of carcinomas and tumors.

A device presently available for sonic image recording is the Sokoloff tube. The front plate of this tube is a thin quartz disc. When the disc is placed in a field of ultrasonic radiation, ultrasonic waves impinging thereon produce a dipole pattern due to the piezoelectric effect, the pattern being distributed over the area of the plate in the form of an image and being capable of scanning by an electron beam. In this way a sound pattern distributed over an area can be converted into a sequence of electrical signals which can then be displayed as an image, for example, by means of a cathode ray tube. For practical reasons, the diameter of the quartz disc used is limited to about -6 cm, but it would be desirable to have available an image recording surface of linear dimensions of at least cm or above, for example, when it is required to observe a wider area of the human body.

SUMMARY OF THE INVENTION The purpose of the present invention is to enable the image recording surface of an ultrasonic image recording system to be increased. This is achieved by providing an ultrasonic image recording system including piezoelectric sound-sensitive means for exposure to a field of ultrasonic radiation to be imaged, in which system the piezoelectric means is in the form of a thin layer of piezoelectric material having charge-sensitive components distributed in an array on the layer of piezoelectric material and pick-up means provided for deriving from the charge-sensitive components electrical signals significant of the level of sound at corresponding points of the ultrasonic field. For example, the piezoelectric layer might comprise a coating deposited on a substrate and the charge-sensitive components could be field-effect transistors.

Supplemental to the above, the pick-up means may include a crossbar arrangement including one group of parallel conductors connected to the sources of the transistors in respective columns of the array and another group of parallel conductors at right angles to the first group connected to the gates of the transistors in respective rows of the array.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a cross section showing a single image point of an image recording surface of a system embodying the invention.

FIG. 2 is a schematic diagram of an ultrasonic image recording system according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I there is shown an ultrasonic image recording surface including a piezoelectric layer in the form of a coating 2 of a suitable material such as cadmium sulphide (CdS) disposed on a substrate 1 which might comprise a plastic foil. The thickness of coating 2 should be between l0 and 50 am. The coating is polycrystalline, the individual crystallites being oriented with the c-axis (in whose direction there is the maximum piezo effect) perpendicular to the substrate 1.

An array or raster of thin film field-effect transistors are formed on the coating 2 by known vapor-coating processes. One such transistor shown in FIG. 1 comprises a drain 3, a source 4, a further coating 5 of CdS and a gate 6. The CdS coating 5 is about 1 pm thick, and the electrodes 3, 4 and 6 are some hundreds of Angstroms thick.

Ultrasonic radiation incident on the image recording surface produces periodically alternating dipole moments at the ultrasonic frequency in the CdS coating 2, and these modulate the current flow between the source and drain of each field-effect transistor. An electrical signal significant of the sound pressure at an image point can be derived by applying suitable voltages simultaneously to the gate and source of the fieldeffect transistor at the image point while the drain is at a fixed potential. The array of field-effect transistors is used to derive signals in succession from the image points of the image recording surface. As is illustrated in FIG. 2, the transistors 5' in the array can be scanned sequentially by a known crossbar arrangement, one group of parallel conductors 7 being connected to the source of the transistors in each column of the array and another group of parallel conductors 8 at right angles to the first group being conneced to the gates of each row of the array.

The transmission of scanning voltages from a potential source 12 from one source conductor to another and from one gate conductor to another is effected at the point or line frequency required for the particular application in which the system is used and could be implemented by, for example, a suitable timer 9 and commutators I0 and I]. The electrical output signal from the transistors is obtained as. a voltage signal at a resistor R situated in a line connecting the drains of all the transistors 5 to earth, is amplified (not shown) and converted to a visual image in a cathode ray tube (television display tube).

For optimum operation, the thickness of the substrate 1 and of the CdS coating 2 should be such that a sound wave impinging from above produces an antinode in the CdS coating 2 and a node at the underside of the substrate ll.

An image recording system embodying the invention may be used both for the direct production of images of structures or, more advantageously, for producing ultrasonic holograms. This second alternative comes to mind because, as mentioned hereinbefore, ultrasonic waves are coherent due to their method of generation.

EXAMPLE A 20 pm thick 10 10cm CdS coating consisting of high-orientation crystallites was vapor-coated on a 1 mm thick glass plate in a high vacuum at 300C. The coating had a resistance of more than 10 cm and was vapor-coated in the form of a piezoelectrically active coating. An array of "X10 CdS field-effect transistors were formed on the coating in the form of a raster by a known process using a masking technique. The piezoelectric modules of the coating of 2.10 Coulombs/dyne and the transconductivity of the transistors of 2.10 A/V together give a minimum detectable sonic radiation intensity of 310 W/cm Scanning of the array of transistors is effected by means of known shift registers controlling the application of scanning pulses to vapor-coated conductors which connect the gates of the transistors in each row and the sources of the transistors in each column. The image represented by the output electrical signal obtained from the system is reproduced in visual form in a conventional television unit. The image sequency is at the maximum time acceptable in medicine, i.e., 1 second. The system is suitable for ultrasonic image recording at an ultrasonic frequency of 10 MHz.

We claim:

1. An ultrasonic image recording system comprising:

piezoelectric sound-sensitive means having a thin layer of piezoelectric material for exposure to a field of ultrasonic radiation to be imaged;

charge-sensitive component means distributed in an array on said layer of piezoelectric material; and,

pick-up means for deriving from the charge-sensitive component means electrical signals significant of the level of sound at corresponding points of the ultrasonic field.

2. A system according to claim 1, wherein said piezoelectric layer comprises a coating deposited on a substrate.

3. A system according to claim 1 wherein said charge-sensitive component means are field-effect transistors.

4. A system according to claim 3, wherein said piezoelectric layer comprises cadmium sulphide and said charge-sensitive component means are cadmium sulphide thin-film field-effect transistors.

5. A system according to claim 4, wherein the pickup means includes crossbar arrangement means c0mprising a first group of parallel conductors connected to the transistor sources in respective columns of the array and a second group of parallel conductors at right angles to the first group connected to the transistor gates in respective rows of the array. 

1. An ultrasonic image recording system comprising: piezoelectric sound-sensitive means having a thin layer of piezoelectric material for exposure to a field of ultrasonic radiation to be imaged; charge-sensitive component means distributed in an array on said layer of piezoelectric material; and, pick-up means for deriving from the charge-sensitive component means electrical signals significant of the level of sound at corresponding points of the ultrasonic field.
 2. A system according to claim 1, wherein said piezoelectric layer comprises a coating deposited on a substrate.
 3. A system according to claim 1 wherein said charge-sensitive component means are field-effect transistors.
 4. A system according to claim 3, wherein said piezoelectric layer comprises cadmium sulphide and said charge-sensitive component means are cadmium sulphide thin-film field-effect transistors.
 5. A system according to claim 4, wherein the pick-up means includes crossbar arrangement means comprising a first group of parallel conductors connected to the transistor sources in respective columns of the array and a second group of parallel conductors at right angles to the first group connected to the transistor gates in respective rows of the array. 